The present invention relates to a printing blanket having a non-extensible backing layer and including at least one relief area, and more particularly, to a printing blanket which may be mounted in a wide variety of printing presses using a number of different lockup mechanisms.
One of the most common commercial printing processes is offset lithography. In this printing process, ink is offset from a printing plate to a rubber-surfaced printing blanket mounted on a blanket cylinder before being transferred to a substrate, such as paper. Typically, the blanket cylinder comprises a chrome or nickel-plated steel cylinder having a longitudinal opening or “gap” therein. An encircling rubber printing blanket is releasably mounted onto the cylinder with opposing ends of the blanket being fed into the cylinder gap and secured by a locking mechanism within the gap. The printing blanket is typically reinforced with a number of fabric and/or rubber plies along with either a fabric or metal backing. The use of a metal backing is often preferable as it prevents stretching of the blanket when it is mounted on the blanket cylinder. The metal backing also provides dimensional stability to the blanket, resulting in high print quality, and eliminates the need for frequent retensioning of the blanket as would be required with conventional fabric-backed blankets.
There are currently a number of different types of lockup mechanisms used in the printing industry to secure printing blankets into the cylinder gap. In most conventional presses, blanket bars are typically secured to each end of the blanket and the ends are inserted into the gap and secured with a lockup device.
In recent years, manufacturers of offset printing processes have equipped newer presses with a “plate” type lockup mechanism which allows the use of metal-backed or non-tensioned blankets and which achieves a very narrow printing gap. The use of the newer presses in combination with a metal-backed blanket provide faster printing speed, higher quality print, longer blanket life, and reduced non-print length compared to standard tensioned blankets which are used with conventional bar lockup devices.
However, blankets containing a metal backing are difficult to mount and tension properly on a blanket cylinder which uses more conventional mounting mechanisms such as single or dual reel rods or “t-bar” type lockups. This is due to the metal at the leading and trailing ends of the blanket which is relatively inflexible and difficult to feed into the cylinder gap. In addition, the stiffness of the metal-backed blankets makes it difficult to mount the blankets around small diameter printing cylinders.
Further, metal backed blankets are expensive to manufacture due to the complex processes required to assemble and finish the blankets to the precise dimensions and specifications required in printing processes.
Accordingly, there is still a need in the art for a printing blanket having a non-extensible backing which provides high print quality, and which may be easily mounted in a variety of printing presses and lock-up mechanisms.